Influence of cation order on crystal structure and microwave dielectric properties in xLi4/3Ti5/3O4-(1-x)Mg2TiO4 (0.6 ≤ x ≤ 0.9) spinel solid solutions

Effect of order/disorder transition on microwave dielectric characteristics is reported to develop a deeper understanding of structure-property relationship in spinel ceramics. Dense xLi4/3Ti5/3O4-(1-x)Mg2TiO4 (0.6≤x≤0.9) spinel ceramics were synthesized and characterized for structural and dielectric properties. The critical order/disorder structural transition was induced when x < 0.8, resulting in the ceramic crystallized into a primary cubic spinel phase, while when x > 0.8, the ceramic crystallized into a disordered face-centered cubic phase. The cation occupation caused this order-disorder transition, which directly influenced the variation in microwave dielectric properties. At x = 0.75 the maximum degree of order was achieved resulting in a maximum quality factor of 55,000 GHz and a near-zero τf = 2.9 ppm/oC. Dielectric properties decreased sharply after x = 0.8 when the disorder face-centered cubic phase started to crystallize. All the results indicated that cation ordering/disordering plays a critical role in determining the optimum microwave dielectric properties in spinel ceramics.